Understanding the complex dynamics controlling marine ecosystem structure and productivity is challenging given the large spatial and temporal scales over which these dynamics occur. A new global database including fisheries stock assessments, research surveys, and ecosystem models has been assembled covering 13 Large Marine Ecosystems. Using these, it is possible to investigate themes directly related to the ecosystem approach to fisheries: (1 the interaction of productivity across fish stocks in ecosystems and the response to fishing pressure, (2 how the trade-off between sustainable yield and ecosystem impacts can be minimized, and (3 analysis of rebuilding rates in over-exploited marine fish stocks, and biological and management drivers of the differential performance of different stocks. There is a central hypothesis associated with each theme: (1 fishing affects the distribution of productivity within the ecosystem but not the total amount, (2 there are irreducible interactions in fishing mortality such that minimizing depletion of less productive stocks will always involve loss of potential yield of more productive stocks and (3 heavily exploited stocks show depensatory responses and rebuild more slowly than assumed in normal compensatory population models. The investigators will conduct analyses across species and ecosystems to determine: mean ecosystem trophic level changes according to catch, survey and stock assessment data and whether the trophic level of catch reflects changes in the ecosystem; correlations in productivity amongst species, trophic levels and functional groups; shifts in community structure from trawl surveys; the extent to which environmental changes or fishing impacts drive productivity; depensation in recruitment and surplus production; the extent of lost yield due to overfishing; catch and assessment data as metrics of ecosystem status; correlations in historical fishing pressure across species, trophic levels and functional groups; the extent to which correlations in fishing pressure can be reduced by spatial management, individual incentives such as catch shares, and changes in fishing technology; rebuilding rates in over-exploited stocks; biological and management drivers of recovery; and management responses to stock over-exploitation. These analyses address fundamental questions of significant intellectual merit about population dynamics, ecosystem structure and productivity, as well as ecosystem interaction and human response.